slowrotor,
forgive me if I misread your second post, but it appears you may want a more simple explanation. Your question seems to suppose that the R22 blades stall rapidly after an engine failure because they operate with a reduced stall margin. The answer is: no.
As all the formulas and experts above have pointed out, there is nothing unusual in the R22s blade loading, nor pitch setting in the hover.
As you are aware, pitch setting is only one of many factors involved in blade stall - the others being speed of the airflow over the airfoil, angle of the airflow hitting the airfoil, G loading, the usual suspects such as density, and many more that Nick et al could rattle off. As such, the pitch setting (such as the 12 to 15 degrees you mention) can be inconsequential without considering all the other factors too.
But the one that concerns your proposition about the blades slowing rapidly and stalling is not really related to the "stall margin" as much as it is to do with the rapid slow down. The blade slows because there is no thrust (engine has failed) to overcome drag. No different to any other helicopter. What is different about the R22 is blade inertia. Blade inertia is very low, so drag is able to rapidly slow the blade (and hence the blade stalls more quickly), where as with an aircraft like the Huey, it's blade has large inertia and will slow down far less quickly than the R22. This is somewhat oversimplified and it ignores pitch angle at the time of engine failure, etc, etc, but you get the picture.
Couple the low inertia blade (ie relatively rapid stall) with the generally low pilot experience levels attracted to the type and is it any real suprise the stats highlight the issue? But that does not mean there is anything wrong with the design - it is more an expected outcome from the factors involved.
Hope that helped.